Biology; Inheritance and variation and selection

What is a chromosome?

Thread like structure of DNA that carries genetic information in the form of genes

what is a gene?

a length of DNA that codes for a protein

what is an allele?

an alternative form of the same gene which gives rise to different characteristics

what is mRNA?

a copy of a gene that moves from the nucleus to the cytoplasm

what is a haploid nucleus

a nucleus that contains a single set of unpaired chromosomes

what is a diploid nucleus

a nucleus containing 2 sets of chromosomes, one pair of each type of chromosome

what is mitosis?

nuclear division that produces genetically identical cells. it is needed in growth, repair and replacement of cells. it is used in asexual reproduction

what is a stem cell

an unspecialized cell (has potential to divide many times while remaining undifferentiated), it divides by mitosis to produce daughter cells that can become specialized for specific functions

what is meiosis?

nuclear division that is involved in producing gametes

define inheritance

transmission of genetic information from generation to generation

define genotype

the genetic makeup of an organism

define phenotype

the observable features of the organism

define homozygous

having 2 identical alleles of a gene

define pure breeding

when 2 identical homozygous individuals breed together

define heterozygous

having 2 different alleles of a particular gene

define dominant

an allele that is expressed where it is present

define recessive

an allele that is only expressed when there is no dominant allele present

what is a carrier?

someone who has a gene for a disease but does not suffer from any symptoms

occurs when a disease is caused by a recessive allele

define monohybrid inheritance

when a single gene is responsible for a phenotype

define polygenic inheritance

when many genes combine to give a phenotype

most phenotypic features are a result of polygenic inheritance

define codominance

if 2 alleles in a heterozygous genotype are expressed in the same phenotype

what is a sex linked characteristic

a gene responsible for phenotype located on sex chromosome, more likely to occur is one sex than the other

what is variation?

differences between individuals of the same species

define continuous variation

data can take a range of values between 2 extremes, it is not categoric and may be affected by both genes and the environment

define discontinuous variation

data can only take particular values with no intermediates, it is categoric and usually only affected by genes

what is phenotypic variation?

different observed characteristics that are caused by genetic and environmental factors

what is genetic variation?

different genes between individuals, may have the same phenotype

define mutation

genetic change

define gene mutation

a random change in the base sequence of DNA

define adaptive feature

an inherited feature that helps and organism to survive and reproduce in its environment

define hydrophyte

a plant that is adapted to live in very wet conditions

define xerophyte

a plant that is adapted to live in very dry conditons

define evolution

a change in adaptive features of a population over time as a result of natural selection